This invention relates to voltage regulation circuitry, and more particularly, to voltage regulation circuitry that can provide an accurate regulated voltage without requiring external voltage reference sources.
Transistors on digital integrated circuits may behave like electrical switches that turn on or off depending on the voltages that are applied at their terminals. Many integrated circuits are based on n-channel metal-oxide-semiconductor (NMOS) transistors and p-channel metal-oxide-semiconductor (PMOS) transistors. An NMOS transistor is a four terminal device having a gate terminal, a drain terminal, a source terminal, and a body terminal.
The gate of an NMOS transistor can be driven to a logic high value (i.e., a positive power supply voltage) to turn the transistor on. When the transistor is on, current may flow from the drain to the source through the channel of the transistor. The channel of the NMOS transistor may be formed beneath the gate of the NMOS transistor. The gate of the NMOS transistor may be driven to ground (e.g., zero volts) to turn the device off. When the device is off, current may stop flowing. PMOS transistors may likewise be turned on and off by applying respective logic low and logic high values on their gates.
As transistors are reduced in size and as supply voltages are decreased with improvements in process technology, it may become difficult to ensure that transistors are fully switched off. For example, even when the gate of an NMOS transistor is grounded, a leakage current may still flow between the drain and the source. Leakage currents can pose problems in modern integrated circuit designs. For example, leakage currents may result in excess power dissipation, undesired discharging of dynamic voltages, robustness issues, and overall performance degradation. Leakage current is typically small in comparison to the normal current of a device that is on.
In certain integrated circuit applications, the presence of leakage may reduce manufacturing yield. In applications that require memory, for example, leakage effects may cause data to be read incorrectly from a memory array. For example, even if a memory cell within the memory array were storing a correct value (e.g., a logic value of “1”), an unsuccessful read operation would result in the reading out of an incorrect value (e.g., a logic value of “0”). The presence of unsuccessful reads from the memory array may render the die that the memory array is formed on defective, making it necessary to discard the die. It may be possible to reduce leakage by providing appropriate bias voltages to the transistors an integrated circuit. Care should be taken, however, to avoid undesirable cost and complexity in bias voltage sources on an integrated circuit. Care should also be taken to ensure that bias voltage sources perform satisfactorily despite changes in fabrication process conditions, operating voltage, and operating temperature (i.e., despite process-voltage-temperature or PVT variations).
It would therefore be desirable to be able to provide improved voltage regulation circuitry such as voltage regulation circuitry for supplying voltages that reduce transistor leakage currents.